The compounds employed in the method of the invention can be prepared by methods analogous to those described by Pollak et al., Tetrahedron 22, 2073 (1966), Miller and Rose, J. Chem. Soc. 1963, 5642, Basu and Rose, J. Chem. Soc. 1963, 5660 (1963), and Bellasio et al., U.S. Pat. Nos. 3,915,968 and 4,016,162.